1. Technical Field of the Invention
This invention relates generally to communication systems and more particularly to RFID systems.
2. Description of Related Art
A radio frequency identification (RFID) system generally includes a reader, also known as an interrogator, and a remote tag, also known as a transponder. Each tag stores identification data for use in identifying a person, article, parcel or other object. RFID systems may use active tags that include an internal power source, such as a battery, and/or passive tags that do not contain an internal power source, but instead are remotely powered by the reader.
Communication between the reader and the remote tag is enabled by radio frequency (RF) signals. In general, to access the identification data stored on an RFID tag, the RFID reader generates a modulated RF interrogation signal designed to evoke a modulated RF response from a tag. The RF response from the tag includes the coded identification data stored in the RFID tag. The RFID reader decodes the coded identification data to identify the person, article, parcel or other object associated with the RFID tag. For passive tags, the RFID reader also generates an unmodulated, continuous wave (CW) signal to activate and power the tag during data transfer.
RFID systems typically employ either far-field technology, in which the distance between the reader and the tag is great compared to the wavelength of the carrier signal, or near-field technology, in which the operating distance is less than one wavelength of the carrier signal, to facilitate communication between the RFID reader and RFID tag. In far-field applications, the RFID reader generates and transmits an RF signal via an antenna to all tags within range of the antenna. One or more of the tags that receive the RF signal responds to the reader using a backscattering technique in which the tags modulate and reflect the received RF signal. In near-field applications, the RFID reader and tag communicate via mutual inductance between corresponding reader and tag inductors.
Currently, RFID readers are formed of separate and discrete components whose interfaces are well-defined. For example, an RFID reader may consist of a controller or microprocessor implemented on a CMOS integrated circuit and a radio implemented on one or more separate CMOS, BiCMOS or GaAs integrated circuits that are uniquely designed for optimal signal processing in a particular technology (e.g., near-field or far-field). However, the high cost of such discrete-component RFID readers has been a deterrent to wide-spread deployment of RFID systems. In addition, there are a number of different RFID standards, each defining a different protocol for enabling communication between the reader and the tag. Discrete RFID reader designs inhibit multi-standard capabilities in the reader.
Therefore, a need exists for a highly integrated low-cost far field RFID reader.